1. Field of the Invention
The present invention relates to a display unit such as a liquid crystal display, more particularly to a liquid crystal display that can compensate changes of chromaticity caused by the switching-over of light source intensity.
2. Description of the Related Art
In recent years, liquid crystal displays have been in widespread use increasingly in various fields. For example, they are liquid crystal front projectors (front-projection type) and liquid crystal rear projectors (rear-projection type) used for presentations by projecting expanded screens of personal computers on screens, liquid crystal display monitors (direct-view type) used as monitors of personal computer screens. Those liquid crystal displays has been well-established as the popular display units next to the most popular cathode-ray tube type.
Since liquid crystal display units are not self-emission type, each of them requires a light source for displaying video images. Each of the direct-view type liquid crystal display monitors which uses a fluorescent tube as its light source switches over the output of the light source by controlling a supply power to provide many functions to cope with user's needs, such as low luminance mode and power saving mode.
On the other hand, in a case of the projection type liquid crystal front projectors and the liquid crystal rear projectors, a high-intensity light source such as a metal halide lamp is used to enable displaying of bright expanded images. However, an output switching-over which is performed for the direct-view type liquid crystal display monitor is scarcely performed in this case, because the shortening of the working life and variation of the emission spectrum may occur by the output switching-over.
Since the light source controlling will be an indispensable function for liquid crystal displays in the future, the above problems should be solved as early as possible. Of those two problems, the shortening of the working life has been improved by some operation methods. For example, the luminance and power of the object display unit is saved to avoid a full use of the display unit capacity, thereby reducing the deterioration of the light source. On the other hand, a variation of the emission spectrum has been unsolved, although it is a fatal problem to disturb the color tones of images for the display unit.